This invention relates to a belt for a sorting machine unit of the so-called "cross-belt" type.
The industrial item sorting sector utilizes sorting machines employing various technologies, such as machines equipped with pushers, tilting dishes, etc.
Other known machines are of the "cross-belt" type, which comprise a small endless conveyor belt or mat installed on a trolley serving as a item carrier and sorting unit, where the said belt is actuated to move in a direction perpendicular to the forward motion of the sorting unit.
The systems based on a "cross-belt" technology enjoy an ever-growing diffusion, thanks to their high productivity coupled with other advantages such as a limited encumbrance and high sorting precision.
Compared to other technologies, the "cross-belt" technology also allows handling an extremely broad range of items, thanks to the fact that the sorting functions are carried out in an active manner, by case-to-case changing of the various parameters such as the acceleration imparted to the item, its unloading time and velocity, depending on the characteristics of the items themselves, thus eliminating the imprecision of the machines based on different technologies, such as those of a tilting-dish type, which unload by gravity.
For the purpose of loading items on the belts of the carrying and sorting units, loading stations are generally provided. These consist of several independent conveyor belts, arranged at an oblique angle to the direction of motion of the sorting unit.
In practice, all these stations constitute the interface between the operators charged with the loading process and the sorting machine itself.
The modern technologies for loading the items include the use of electronic devices capable of automatically verifying the dimensions and characteristics of the items and calculating, for each of them, the optimum accelerations and transit velocities.
The control of the functionality of the loading station generally serves the purpose of assigning each item to a sorting unit, and positioning the item at the center of the belt of that unit.
This positioning step is most important for a favorable final result, as any items loaded in erroneous positions may cause jamming along the sorting path, with a resulting abnormal operation of the machine and damage to the items. The items may even fall off the sorting unit, or, as in the most common case, assume anomalous trajectories during the unloading phase at the destination, with a consequent jamming in the exit devices and/or with sorting errors.
Although the latest systems utilize highly sophisticated technologies and equipment to ensure a precise positioning of the items, some loading errors occasionally still occur, wherein "error" involves an inability of an item to find its ideal position on the sorting unit.
These errors are generally generated by the unpredictable behavior of certain objects, both during the loading phase and while passing from the loading station to the carrying and sorting mat or belt.
In order to minimize these shortcomings, the present state of the art resorts to the following devices:
when the introduction belt is inclined in a horizontal plane with respect to the direction of motion of the sorting unit, the item is loaded onto the still-moving sorting unit with a velocity vector including some components congruent with the forward velocity of the sorting unit, so that the item may be deposited on the belt at a relative velocity of essentially nil; PA1 beside the path of the sorting machine, in front of the loading stations, some barriers are installed which prevent any objects with a low friction coefficient from being pushed off the sorting unit, in a direction perpendicular to the direction of motion of the unit; PA1 some retaining curbs are installed on the sorting units, separate from the mat, to prevent any items with a low friction coefficient from sliding off in the direction of motion of the unit, and thus dropping off the unit in either the forward or rearward direction; PA1 conveyor belts made of highly adherent materials are used, so as to reduce any undesirable effects when handling items with a low friction coefficient.
However, all of the expedients described above cannot always prevent the occurrence of anomalous situations, so that it occasionally still happens that some items are improperly positioned on the mats.
For example, limp items such as plastic bags of a large size with respect to the volume of their contents, tend to glide in the direction of motion of the machine, so that the use of any fixed banks on the carrying units may have negative effects.
The bags may in effect position themselves so as to partially pile up on the bank, which may in an unloading phase slow the item's motion by friction, thus adversely affecting its trajectory.
Moreover, the mats, friction coefficient varies in use due to the dirt accumulating on its surface or because of different conditions of humidity, with the result that the behavior of the items may in an unloading phase be affected even to a considerable extent.
Some known conveyor belts also carry a row of ledges arranged in a direction perpendicular to the direction of motion of the mat, i.e., parallel to the direction of motion of the sorting unit. These ledges are used when the conveyor belt is severely inclined, so as to prevent a slippage of the items being carried.
Other known rotating mats have a curb affixed to their lower (interior) surface (in contact with the supporting rollers), which curb slides in a groove provided in the supporting rollers and functions as a guide to keep the mat centered on the rollers.